The present embodiments relate to ultrasound imaging. In particular, jittering in medical diagnostic ultrasound imaging is reduced.
In ultrasound imaging, spatial compounding is used in extended field of view and/or steered compounding for speckle reduction. Different component frames of data associated with spatial differences (e.g., different steering angle or transducer position) are acquired and combined. However, this spatial compounding suffers from motion artifacts. Because frames are acquired at different times, and each frame takes a certain amount of time to acquire, movement of the tissue or probe can cause mis-registration between frames. When frames are compounded, the compounded image will be smeared or blurred. If the user is searching for a target region by moving the transducer, the blurring is even more pronounced.
To reduce blurring, the mis-registration errors between compounding frames caused by motion are corrected by registering the component frames to each other prior to compounding. Global and/or local displacement information between two images is estimated, such as by cross-correlation, block matching, maximum brightness, and/or feature extraction and tracking. One or both images are warped and/or aligned to make them congruent with each other. However, these solutions assume that the component frames have correlated speckle patterns or are fairly similar. The detail features (e.g., speckle pattern) for images acquired from different steering angles may be uncorrelated due to the differences between a skewed point spread function (steered beam) and a non-skewed point spread function (non-steered beam). Features, like acoustic shadows, have angle and position dependency per incident angle of ultrasonic wave, causing mis-registration. Transducer motion in an elevation direction or tilting may result in the frames having no speckle correlation and similarity at all, causing registration failure. During the scan, the clinicians may squeeze the tissue by putting some pressure on the transducer, causing mis-registration.
Variation in the imaging may cause jittering artifacts in the motion correction. Changes in the steering angle and/or region to be imaged may result in variation in registration, creating an “earthquake” effect.